This invention relates to semiconductor lasers fabricated after device growth utilizing impurity induced disordering (IID) and more particularly the fabrication and design of multi-emitter semiconductor laser arrays having minimal electrical and thermal crosstalk and high efficiency useful for high speed raster output scanners (ROS) and laser printing applications.
The ability to fabricate closely spaced independently addressable laser sources is important for many applications such as optical disk technology, laser printing, optical interconnection and fiber optic communications. It is often desirable to have the laser elements of a laser array in as close proximity as possible in order to simplify optical system design. For optical interconnections, and especially when spacing between laser elements is only a few microns, it is highly desirable to mount the devices with their p-side up in order to simplify the separation of electrical connection to the laser devices. However, this places constraints on device performance in order to achieve CW operation. Previous attempts have been made to provide separate contacting of laser elements of such devices but these devices were not capable of CW operation. In addition, the optical and carrier confinement was insufficient to prevent coupling and phase locking between sources.
Acceptable CW performance has been obtained in p-side up configuration with etch and regrown buried heterostructure lasers, but reliability and yield remain key issues in production of high density laser arrays by this technique.
Single emitter lasers generally of the III-V material regime, e.g., GaAs/GaAlAs, have a designed higher refractive index cavity which is formed between laterally adjacent regions of comparatively lower refractive index. It is known to produce such optical cavities by means of nonplanar growth mechanisms, such as a channel or mesa in the laser substrate or by means of impurity induced disordering (IID) as exemplified in Holonyak U.S. Pat. No. 4,378,255 . As taught in this patent, a semiconductor structure containing a quantum well feature, such as a multiple quantum well, undergoes compositional disordering due to impurity diffusion. Diffusion of an impurity into spatially separated regions of the quantum well feature will cause an intermixing of Al and Ga in the well feature so that the average refractive index through the region of these layers subjected to disordering by diffusion will have a lower index of refraction compared to undisordered regions including the central region between the designated spatially separated regions. Thus, the central region may be utilized as an optical waveguide cavity for lasing and/or light propagation.
It has been shown that silicon impurity induced disordering (Si-IID) technology is capable of producing low threshold buried heterostructure lasers with power conversion efficiencies on the order of 50% at normal power levels. This high level of performance permits these types of devices to be mounted p-side up and CW operated. In addition, it has been shown that laser arrays of this type with center-to-center separations as low as 4 .mu.m with a single contact addressing electrode exhibit a high degree of uniformity and do not exhibit phase locked operation as a result of the strong refractive index waveguiding mechanism provided via Si-IID. Therefore, this technology should also be considered for high density laser arrays wherein each of the laser elements are independent addressable if the problems of optical and electrical crosstalk, such as modulation or oscillation crosstalk, between independently operated laser elements in the array does not present serious problems for a particular application or such problems can be suppressed to an acceptable level.
The use of laser of LED arrays for laser printers having flying spot scanners or raster output scanners (ROS) have been suggested previously, as exemplified in U.S. Pat. Nos. 4,445,125; 4,474,422 and patent application Ser. No. (D/86364), assigned to the same assignee as herein, because of their small size, low power requirements, longevity, ease of fabrication, low cost and sensitivity in the infrared spectra for exposure of infrared photoreceptors to create or write a latent electrostatic image on the charged photoreceptor surface. There is also the advantage of scanning simultaneously more than one scan line at a time with two or more beams from a monolithic semiconductor laser source, as exemplified in U.S. Pat. No. 4,474,422 and in patent application Ser. No. (D/86364).
It is a principal object of this invention to use IID in providing high density arrays of independently addressable semiconductor laser sources, particularly useful in ROS and laser printing applications and also applicable in other applications, such as optical recording playback systems.